A twine delivery needle arrangement of a large square baler includes needles mounted to a needle yoke or frame which is mounted to a baling chamber for pivoting so that twine-carrying tip sections of the needles move upwardly through the baling chamber from a location below the baling chamber to deliver respective lengths of twine to knotters forming part of a knotter table mounted to a top wall of the baling chamber. The needle yoke is U-shaped and includes a pair of parallel arms respectively joined at right angles to opposite ends of a cross tube that extends beneath the baling chamber. The number of needles used depends on the number of loops needed to adequately bind a bale of a given size, with common bale sizes requiring four or six loops and thus four or six needles, for example. Each needle includes a base mounted to the cross tube by a clamp which has four bolts. The cross tube of the needle yoke extends transversely below the baling chamber, with the parallel arms of the yoke having upper ends pivotally mounted on opposite sides of the baling chamber for rotation about a horizontal transverse axis. The needle yoke arms are respectively coupled to opposite ends of a knotter gear drive shaft of the knotter table by four-bar linkages. One tie cycle is 180° rotation of the needle yoke over 360° rotation of the knotter gear drive shaft, which in a known design operates at 45 RPM. During a first half of a tying cycle, the knotter gear drive shaft rotates 180° with the needle yoke initially rotating 90° so as to carry the needles upwardly from a home position (0° needle yoke rotation), wherein the twine-carrying tip sections of the needles are beneath the baling chamber, to a top dead center (TDC) position, wherein the twine-carrying tip sections of the needles project into the knotter table. During a second half of the tying cycle, the motion of the needle yoke reverses and it rotates 90° back to the home position. This movement of the needles during a tying cycle is accommodated by vertically aligned needle slots, respectively provided in the bottom and top walls of the baling chamber, a bottom wall of the knotter table and in a baler plunger positioned in a rearward compaction stroke (U.S. Pat. No. 8,069,780, granted Dec. 6, 2011 clearly shows needle clearance slots provided in a plunger and is incorporated herein by reference in its entirety).
A typical twine-delivery needle of a known design is constructed of metal and weighs about 20 pounds. A known baler is equipped with six twine-delivery needles which are carried by a yoke which weighs about 150 pounds. Therefore, the total weight of the needle arrangement (weight of needles plus weight of needle support yoke) is about 270 pounds, resulting in substantial torque being required to get the needle system moving, and, thereafter, in substantial inertia being developed as the needles move between the home and TDC positions causing over-running unless a damper is used. Since the needle arrangement is linked for being driven by the knotter gear drive shaft, substantial cross bracing is required between the drive shaft and the pivot structure of the needle yoke in order to provide sufficient strength for accommodating the initial torque requirement. Also, the yoke arms must be constructed to have sufficient rigidity to prevent the yoke from twisting due to the initial torque requirement. The aforementioned U.S. Pat. No. 8,671,834, granted Mar. 18, 2014 discloses a needle arrangement of the above-described type.
Another drawback of using metal needles is that, if the needles are stranded in the bale chamber or are mistimed relative to the stroke of the plunger for compacting crop material in the baling chamber, the plunger will contact the needles and cause major damage to one or more of the needle arrangement, the plunger system and the knotter table, which includes the knotter gear drive shaft.
The problem to be solved then is that of reducing the weight of the needle arrangement while maintaining sufficient strength in the needles for preventing them from being deflected sideways resulting in interference and possible damage.